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Ceramic zinc stannate, Zn(_2)SnO(_4), was prepared from 1SnO(_2):2ZnO mixture using powders of the highest commercially available purity. The solid state reaction between the ZnO and the SnO(_2), thought to be an evaporation-recondensation mechanism, was found to start at ~ 900 ˚C (12 hours heating, rate 5 ˚C min(^-1)). However, the reaction did not go to completion in the timescale of the experiment unless the temperature was raised to~1300 C. In this case mono-phase, polycrystalline Zn(_2)SnO(_4) was produced, as confirmed by X-ray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray analysis (EDAX). Further evidence for these reaction temperatures was obtained from thermal analysis experiments. As-sintered, Zn(_2)SnO(_4) was insulating (σ — 10(^19) Ω(^-1) cm(^-1)) although it could be made conductive, by a reduction heat-treatment. This entailed refiring the sintered pellets of Zn(_2)SnO(_4) in an atmosphere of mixture gas (25% H(_2) + 75% N(_2)) at ~ 450 ˚C for 14 hours (heating rate of 10 C min(^-1)). This reduced the conductivity to values of σ~1 x 10(^-2) Ω(^-1) cm(^-1) . XRD failed to reveal any changes in the phase of the material after the reduction treatment. Several dopants were investigated, the most successful of which was in, using a vapour phase method. Doping with In this way gave a significant change in the colour from white to dark grey together with a reduction in electrical resistivity, without recourse to further heating treatments. No change in the usual phase of the Zn(_2)SnO(_4) was detected. Doping with group V oxides, such as Nb(_2)O(_5), V(_2)O(_5) etc, produced changes in the colour from white to dark grey, but no reduction in the resistivity, unless further heating treatments were carried out in reducing ambients. When high concentrations of Nb were introduced an additional phase, possibly Nb(_2)Sn(_2)O(_7) was observed by XRD. Thin film Zn(_2)SnO(_4) was prepared by Electron Beam Evaporation using Zn2Sn04 sintered powder as the evaporant material. The thin films were deposited onto glass substrates, at a range of substrate temperatures between room temperature and 250 ˚C. XRD was used to confirm the formation of Zn(_2)SnO(_4), and provide estimates for the grain size, which varied from 20 to 25 nm. RHEED studies indicated that the grain size increased as the substrate temperature was increased. SEM revealed that the thin films were flat and uniform, with no cracks. The optical transmission of the thin films was about 88% for films deposited at 200 ˚C, but decreased significantly as the substrate temperature was decreased. The spectral dependence of complex refractive index (n&k) suggested that true thin film formation did not take place until the substrate temperature exceeded ~ 150 ˚C, and that the material was apparently a direct gap semiconductor with a band gap energy of ~1.95 eV. It was found that the main carrier transportation mechanism for doped, un- doped, and thin films of Zn(_2)SnO(_4) was variable range hopping, with a temperature dependence of the form exp(To/T)'^\ This result was consistent with Hall effect measurements, where high, temperature independent carrier concentrations of about 10(^17) cm(^-3) were obtained, along with low values of carrier mobility ( ~ 1 cm(^2) v(^-1) sec(^-1)) that obeyed the same temperature dependence as the conductivity, [exp(To/T)(^1/4)].

The environmental concerns related to the production of cement in terms of the energy consumption and the emission of CO2 lead to the search for more environmentally viable alternatives to cement. One of those alternative materials is alkali-activated slag (AAS) where ground granulated blast furnace slag is used not as a partial replacement to cement but as the sole binder in the production of concrete. The performance of alkali-activated slag concrete with sodium silicate (water glass) as an activator was studied. The scope of the work covered seven mixes: a normal strength OPC control mix, a blended OPC/Slag mix of similar compressive strength but of lower water to binder ratio, a second OPC control mix of a water to binder ratio similar to that of the OPC/Slag mix, and four alkali-activated slag mixes of the same binder content and the same water to binder ratio as those of the second OPC mix. The AAS mixes were prepared with slag as the sole binder, activated with water glass at two dosages, 4% and 6% Na2O (by weight of slag). Two types of water glass were used, one in a solution form and the other in a solid granules form. The two forms of the activator used were also of different silicate modulus (Ms); 1.65 for the solution form and 1.0 for the granule form. Different curing regimes were used including normal water curing, air dry curing and accelerated autoclave heat curing. The fresh concrete properties studied were setting time, workability and air content. The engineering properties studied were compressive strength, splitting tensile strength, flexural strength, dynamic modulus of elasticity and ultrasonic pulse velocity and drying shrinkage. The durability potential of alkali-activated stag concrete was investigated by testing for oxygen permeability, chloride penetration resistance, porosity, carbonation, and alkali-silica reaction. The hydration of alkali-activated slag was studied using x-ray diffraction and thermogravimetry techniques. Alkali-activated slag concrete was found to achieve good workability which was, comparable to that of OPC and OPCfslag concrete. The increase of the Na2O dosage resulted in a lower workability and the activator with higher silicate modulus exhibited lower workability. AAS concrete however, sets rapidly if not controlled by the addition of lime. The main hydration products in the AAS systems were C-S-H (I) and hydrotalcite as observed in the XRD patterns with autoclaving resulting in the formation of a more crystalline C-S-H gel and the possible formation of xonotlite. The mechanical properties of AAS concrete are highly influenced by the activator's silicate modulus and the Na2O dosage where strength was found to be higher with the higher modulus and dosage. The AAS concrete is very sensitive to curing and dry curing resulted in a reduction in strength for AAS concrete much more than that for OPC concrete. Accelerated curing (autoclave) increased the initial gain of strength in AAS concrete but eventually gave results close to those of water curing. Using a waterglass activator with Ms = 1.65 and 6% Na2O resulted in the highest drying shrinkage where as it is lower when the dosage is less and the modulus is lower. Autoclave curing of AAS concrete reduces the drying shrinkage as it causes the formation of more crystalline products of hydration. The increase of the Na2O dosage in AAS concrete, where the activator has an M. = 1.0, results in a decrease in porosity, but in the case of the AAS concrete, with the activator having Ms = 1.65, the porosity increases with the increase of the Na20 dosage. Dry curing increases the porosity of all the concrete mixes. The porosity test results are influenced by the sample preconditioning prior to testing. The alkali-silica test results show that replacing 60% OPC by slag reduces the expansion of concrete prisms containing reactive aggregates. They also indicate that AAS concrete has low susceptibility to ASR expansion because of stronger binding of alkalis in the hydration products. The carbonation test results show that OPCIslag concrete undergoes higher carbonation than OPC concrete with the same w/c ratio. AAS concrete with low compressive strength around 40 MPa has higher carbonation compared to OPC concrete of the same grade while the carbonation is lower with higher strength.

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Several methods of strengthening, including surface precipitation of low solubility particles, vapour treatment, ion-exchange, chemical vapour deposition (CVD) and combination treatments, have been investigated to improve the pristine strength of commercially available container and related glass compositions; their relative applicability in container manufacture has also been evaluated and discussed. As a part of this, a wide range of soda lime silica compositions, that includes typical container glass specifications, have been investigated to study their crystallisation behaviour in terms of the effect of nucleating agent, viscosity, time and temperature. Significant flexural strength enhancement of 16 to 163 % has been achieved for the processes studied, with a maximum of ~ 500 MPa and ~ 400 MPa for glasses using lithium ion exchange and exposure to LiBr and/or AlBr3 vapour respectively. Treatment times are short, compared to those currently used in industry. The mechanism of strengthening relies on surface compression by production of a glass skin or surface crystallised phase(s) having a low thermal expansion coefficient than the bulk of the glass. The physical properties of the glasses have been characterised by differential thermal analysis (DTA) and X-ray diffraction (XRD) as well as other methods such as high temperature viscometry and dynamic secondary ion mass spectroscopy (SIMS).

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